1. Field
One embodiment of the present invention relates to a magnetic recording medium capable of recording at high density and a method of manufacturing the magnetic recording medium.
2. Description of the Related Art
In the information-oriented society in recent years, the amount of data that needs to be stored in a recording medium has been continually increasing. To keep up with the increase in amount of data, there has been a demand for a recording medium and a recording apparatus with a dramatically high recording density. As regards a hard disk for which there is an increasing demand as a high-capacity and inexpensive magnetic recording medium, it is predicted that a recording density of one terabits per square inch or more, which is about ten times higher than the current recording density, will be required several years after.
In an existing magnetic recording medium used in a hard disk, one bit is recorded in a specific region of a thin film made of polycrystals of fine magnetic grains. To raise the recording capacity of the magnetic recording medium, therefore, the recording density must be increased. For this purpose, it is effective to reduce a recording mark size usable in recording per bit. If, however, the recording mark size is simply reduced, effect of recording noise caused by the shape of fine magnetic grains cannot be neglected. Instead, if the fine magnetic grains are further reduced in size, it is impossible to maintain the data recorded in fine magnetic grains at an ordinary temperature due to a problem of thermal fluctuation.
To avoid these problems, it is proposed to use a patterned medium in which dots of recording material are separated by a non-recording material in advance so as to perform read and write using a single recording dot as a single recording cell (see U.S. Pat. No. 5,956,216).
Also, as to a recent improvement in the track density of a hard disk drive (HDD), a problem of interference between adjacent tracks becomes obvious. In particular, a serious technical subject is reduction of write blurring due to fringe effect of magnetic fields from a write head. The discrete track recording-type patterned medium (DTR medium) in which recording tracks are physically separated is capable of reducing a side erase phenomenon in writing or a side read phenomenon in reading, and is capable of enhancing the track density. Therefore, the DTR medium is expected as a magnetic recording medium capable of providing a high recording density (see Jpn. Pat. Appln. KOKAI Publication No. 7-85406).
It should be noted that the term patterned medium herein includes the DTR medium since the DTR medium is also one form of the patterned media.
In conventional patterned media, a method is mainly adopted in which a ferromagnetic recording layer is etched to reach an underlayer to completely cut off the magnetic interference between magnetic patterns. However, the flying height of a head of a current hard disk drive is less than 10 nm, and stable flying of the head is not obtained if recesses having a depth corresponding to the thickness of the ferromagnetic recording layer of 20 nm to 30 nm are formed. This problem is solved by filling the recesses between the magnetic patterns with a nonmagnetic layer to flatten the surface. However, increase in the depth of the recesses leads to increase in process time.
In view of this, a method has been proposed in which recesses shallower than the thickness of the ferromagnetic recording layer are formed. However, the magnetic interference between magnetic patterns is not completely cut off only by processing a part of the ferromagnetic recording layer to form shallow recesses, which arises such a problem that signals of the adjacent track are detected as noise.
Also, a method is known in which a part of the ferromagnetic recording layer is reacted with a reactive gas or reactive solution containing halogen to chemically modify the recording layer to form a nonmagnetic layer, thereby forming magnetic patterns separated by the nonmagnetic layer (see Jpn. Pat. Appln. KOKAI Publication No. 2002-359138). However, in this method, the halogen left unremoved in the nonmagnetic layer causes corrosion.